Energy-efficient personal audio device output stage with signal polarity-dependent power supply update rate

ABSTRACT

A charge pump power supply may comprise a plurality of capacitors and a switching circuit for switching the capacitors to provide a first voltage or a second voltage in accordance with the select input. The charge pump power supply may have a signal polarity input for indicating a polarity of an output audio signal. Switches for switching one or more capacitors providing a first polarity voltage in a then-current operating mode may be configured to switch at a greater frequency than switches for switching one or more capacitors providing a second polarity voltage responsive to the signal polarity input indicating a positive polarity of the output audio signal. Switches for switching one or more capacitors providing the first polarity voltage in a then-current operating mode are configured to switch at a lesser frequency than switches for switching one or more capacitors providing the second polarity voltage responsive to the signal polarity input indicating a negative polarity of the output audio signal.

FIELD OF DISCLOSURE

The present disclosure relates in general to circuits for personal audiodevices such as wireless telephones and media players, and morespecifically, to systems and methods for conserving energy in a personalaudio device output stage by controlling an output stage power supplybased on a polarity of an audio signal.

BACKGROUND

Personal audio devices, including wireless telephones, such asmobile/cellular telephones, cordless telephones, mp3 players, and otherconsumer audio devices, are in widespread use. Such personal audiodevices may include circuitry for driving a pair of headphones or one ormore speakers. Such circuitry often includes a power amplifier fordriving an audio output signal to headphones or speakers, and the poweramplifier may often be the primary consumer of power in a personal audiodevice, and thus, may have the greatest effect on the battery life ofthe personal audio device. In devices having a linear power amplifierfor the output stage, power is wasted during low signal level outputs,because the voltage drop across the active output transistor plus theoutput voltage will be equal to the constant power supply rail voltage.Therefore, amplifier topologies such as Class-G and Class-H aredesirable for reducing the voltage drop across the output transistor(s)and thereby reducing the power wasted in dissipation by the outputtransistor(s). In such topologies, power consumption is reduced byemploying a power supply, typically a charge pump power supply, whichhas selectable modes of operation based on an amplitude of an audiooutput signal of the power amplifier, wherein each of the selectablemodes provides a different bi-polar supply voltage across power supplyrails of the power amplifier.

While such topologies are more energy efficient than predecessortopologies, such topologies may still waste power. For example, when anaudio output signal is of a positive polarity, load current to the audiooutput is typically delivered only from a positive supply rail of thepower amplifier, and a quiescent power may be wasted in maintaining avoltage on the negative supply rail by the power supply. Similarly, whenan audio output signal is of a negative polarity, load current to theaudio output is typically delivered only from a negative supply rail ofthe power amplifier, and a quiescent power may be wasted in maintaininga voltage on the positive supply rail by the power supply.

Therefore, it would be desirable to provide a power amplifier circuitfor a consumer audio device that has improved efficiency and reducedpower dissipation, while maintaining a specified full-signal outputlevel capability.

SUMMARY

In accordance with the teachings of the present disclosure, thedisadvantages and problems associated with existing approaches todriving audio output signals may be reduced or eliminated.

In accordance with embodiments of the present disclosure, an audioamplifier circuit for providing an output signal to an audio transducermay include a power amplifier and a charge pump power supply. The poweramplifier may have an audio input for receiving an audio input signal,an audio output for providing the output signal, and a power supplyinput. The charge pump power supply may provide a power supply voltageto the power supply input, wherein the power supply voltage has a firstpolarity voltage relative to a common-mode voltage and a second polarityvoltage relative to the common-mode voltage such that the power supplyvoltage equals a difference between the first polarity voltage and thesecond polarity voltage. The charge pump power supply may have a selectinput for selecting an operating mode of the power supply. In a firstoperating mode, the power supply voltage may be equal to a firstvoltage, and in a second operating mode the power supply voltage may besubstantially equal to a rational fraction of the first voltage. Thecharge pump power supply may comprise a plurality of capacitors and aswitching circuit for switching the capacitors to provide the firstvoltage or the second voltage in accordance with the select input. Thecharge pump power supply may have a signal polarity input for indicatinga polarity of the output signal. Switches for switching one or morecapacitors providing the first polarity voltage in a then-currentoperating mode are configured to switch at a greater frequency thanswitches for switching one or more capacitors providing the secondpolarity voltage responsive to the signal polarity input indicating apositive polarity of the output signal. Switches for switching one ormore capacitors providing the first polarity voltage in a then-currentoperating mode are configured to switch at a lesser frequency thanswitches for switching one or more capacitors providing the secondpolarity voltage responsive to the signal polarity input indicating anegative polarity of the output signal.

In accordance with these and other embodiments of the presentdisclosure, a method for providing an output signal to an audiotransducer may include providing by a charge pump power supply a powersupply voltage to a power supply input of a power amplifier having anaudio input for receiving an audio input signal and an audio output forproviding the output signal. The power supply voltage may have a firstpolarity voltage relative to a common-mode voltage and a second polarityvoltage relative to the common-mode voltage such that the power supplyvoltage equals a difference between the first polarity voltage and thesecond polarity voltage, wherein the common-mode voltage is equal to amean of a maximum first polarity voltage and a minimum second polarityvoltage. The charge pump power supply may have a select input forselecting an operating mode of the power supply. In a first operatingmode, the power supply voltage may be equal to a first voltage, and in asecond operating mode the power supply voltage may be substantiallyequal to a rational fraction of the first voltage. The charge pump powersupply may comprise a plurality of capacitors and a switching circuitfor switching the capacitors to provide the first voltage or the secondvoltage in accordance with the select input. The charge pump powersupply may have a signal polarity input for indicating a polarity of theoutput signal. The method may also include operating switches forswitching one or more capacitors providing the first polarity voltage ina particular operating mode at a greater frequency than switches forswitching one or more capacitors providing the second polarity voltageresponsive to the signal polarity input indicating a positive polarityof the output signal. The method may further include operating switchesfor switching one or more capacitors providing the first polarityvoltage in the particular operating mode at a lesser frequency thanswitches for switching one or more capacitors providing the secondpolarity voltage responsive to the signal polarity input indicating anegative polarity of the output signal.

Technical advantages of the present disclosure may be readily apparentto one skilled in the art from the figures, description and claimsincluded herein. The objects and advantages of the embodiments will berealized and achieved at least by the elements, features, andcombinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are examples and explanatory and arenot restrictive of the claims set forth in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 is an illustration of an example personal audio device, inaccordance with embodiments of the present disclosure;

FIG. 2 is a block diagram of selected components of an example audiointegrated circuit of a personal audio device, in accordance withembodiments of the present disclosure;

FIG. 3 is a schematic diagram depicting an example charge-pump powersupply, in accordance with embodiments of the present disclosure;

FIGS. 4A-4D are schematic diagrams depicting individual charge-pumpclock phases for operating modes of the charge-pump power supply circuitdepicted in FIG. 3, in accordance with embodiments of the presentdisclosure; and

FIGS. 5A-5D are schematic diagrams depicting individual charge-pumpclock phases for operating modes of the charge-pump power supply circuitdepicted in FIG. 3, in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

FIG. 1 is an illustration of an example personal audio device 1, inaccordance with embodiments of the present disclosure. FIG. 1 depictspersonal audio device 1 coupled to a headset 3 in the form of a pair ofearbud speakers 8A and 8B. Headset 3 depicted in FIG. 1 is merely anexample, and it is understood that personal audio device 1 may be usedin connection with a variety of audio transducers, including withoutlimitation, headphones, earbuds, in-ear earphones, and externalspeakers. A plug 4 may provide for connection of headset 3 to anelectrical terminal of personal audio device 1. Personal audio device 1may provide a display to a user and receive user input using a touchscreen 2, or alternatively, a standard LCD may be combined with variousbuttons, sliders, and/or dials disposed on the face and/or sides ofpersonal audio device 1. As also shown in FIG. 1, personal audio device1 may include an audio integrated circuit (IC) 9 for generating ananalog audio signal for transmission to headset 3 and/or another audiotransducer or speaker.

FIG. 2 is a block diagram of selected components of an example audio IC9 of a personal audio device, in accordance with embodiments of thepresent disclosure. As shown in FIG. 2, a microcontroller core 18 maysupply a digital audio input signal DIG_IN to a digital-to-analogconverter (DAC) 14, which may in turn supply an analog audio inputsignal to a first amplifier stage A2 that may be operated from a fixedvoltage power supply. In the embodiments represented by FIG. 2, theinput to DAC 14 may be a digital audio source, but that is not alimitation of the present disclosure, as the techniques of the presentdisclosure may be applied to an audio amplifier having a purely analogsignal path. The signal at the output of first amplifier stage A2 may beprovided to an attenuator 16 that receives a volume control signal andattenuates the signal accordingly. Attenuator 16 may be a digitalpotentiometer having control provided from a microcontroller or otherdigital control circuit responsive to a user interface, volume knobencoder or program command, or attenuator 16 may be an analogpotentiometer that provides the volume control signal as an outputindication from a secondary deck (separate potentiometer circuit coupledto the common shaft or other mechanism). While an attenuator 16 is shownas the volume control mechanism, it is understood that an equivalentvolume control may be provided by a programmable resistor or adjustablegain in the feedback of amplifier A2 or another amplifier stage in thesignal path. A controller 27 may generate predriver signals PDRV andNDRV based on the audio input signal V_(IN) received from attenuator 16,and a final power amplifier stage A1 may amplify the predriver signalsPDRV and NDRV to provide an audio output signal V_(OUT), which mayoperate a speaker, headphone transducer, and/or a line level signaloutput.

In some embodiments, the power supply voltage V_(SUPPLY) may comprise asingle-ended voltage referenced to a ground voltage having a common-modevoltage equal to one-half of a maximum power supply voltage, andaccordingly wherein the positive polarity voltage has a maximum equal tothe maximum power supply voltage and the negative polarity voltage has aminimum equal to the ground voltage. In other embodiments, the powersupply voltage V_(SUPPLY) may comprise a differential voltage having acommon-mode voltage equal to a mean of a maximum positive polarityvoltage and a minimum negative polarity voltage. In both of theseembodiments, the audio output signal V_(OUT) may be considered to have apositive polarity when it is greater than the common-mode voltage and tohave a negative polarity when it is lesser than the common-mode voltage.In embodiments in which V_(SUPPLY) is a single-ended supply having aquiescent voltage substantially differing from ground, a capacitor maybe utilized to couple the output of amplifier A1 to a transducer or linelevel output.

A charge pump power supply 10 may provide the power supply rail inputsof amplifier A1 and may receive a power supply input, generally from abattery or other power supply, depicted as battery terminal connectionsVBATT+ and VBATT−. A mode control circuit 12 may supply a mode selectsignal to charge pump power supply 10 that selects an operating mode ofcharge pump power supply 10 as described in greater detail elsewhere inthis disclosure. Also, output voltage V_(SUPPLY) of charge pump powersupply 10 may be adjusted according to expected and/or actual audiosignal levels at the amplifier output according to the techniquesdisclosed elsewhere in this disclosure.

When low signal levels exist and/or are expected at amplifier outputV_(OUT), the power efficiency of the audio output stage may be improvedby varying the supply voltage V_(SUPPLY) in conformity with the outputsignal V_(OUT) or a signal (e.g., volume control signal Volume, audioinput signal V_(IN)) indicative of the output signal V_(OUT). In orderto determine the actual and/or expected signal amplitudes at the outputof amplifier A1, the volume control signal Volume, audio output signalV_(OUT), and/or audio input signal V_(IN) may be supplied to modecontrol circuit 12 for controlling the differential power supplyV_(SUPPLY) generated by charge pump power supply 10, in conformity withthe expected amplitude of the output signal.

In addition, mode control circuit 12 may supply a polarity signal tocharge pump power supply 10 indicative of a polarity of audio outputsignal V_(OUT). In some embodiments, mode control circuit 12 maydetermine the polarity of audio output signal V_(OUT) based on a signbit of digital audio input signal DIG_IN. In other embodiments, modecontrol circuit 12 may determine the polarity of audio output signalV_(OUT) by comparing a load current of a load coupled to the output ofamplifier A1 to a quiescent current through at least one driving deviceof amplifier A1. In yet other embodiments, mode control circuit 12 maydetermine the polarity of audio output signal V_(OUT) based on a voltagedifference between supply voltage V_(SUPPLY) and one or more of batteryvoltage VBATT+ and VBATT−.

In these and other embodiments, currents generated by switching devicesof amplifier A1 may be controlled based on the polarity of audio outputsignal V_(OUT). For example, power amplifier A1 may include at least oneswitching device for generating the positive polarity voltage of audiooutput signal V_(OUT) and at least one switching device for generatingthe negative polarity voltage of audio output signal V_(OUT) based onthe audio input signal. As mentioned above, audio IC 9 may include acontroller 27 configured to generate predriver signals PDRV and NDRVbased on the audio input signal V_(IN) received from attenuator 16.Predriver signal PDRV may drive the at least one switching device forgenerating the positive polarity voltage of audio output signal V_(OUT)and predriver signal NDRV may drive the at least one switching devicefor generating the negative polarity voltage of audio output signalV_(OUT). Responsive to a positive polarity of audio output signalV_(OUT) (as indicated by the polarity signal generated by mode controlcircuit 12 or another component of audio IC 9), controller 27 maygenerate predriver signals PDRV and NDRV such that the at least oneswitching device for providing the positive polarity voltage operates ata first current and responsive to a negative polarity of audio outputsignal V_(OUT), the at least one switching device for providing thepositive polarity voltage operates at a second current less than thefirst current. Similarly, responsive to a negative polarity of audiooutput signal V_(OUT), controller 27 may generate predriver signals PDRVand NDRV such that the at least one switching device for providing thenegative polarity voltage operates at a first current and responsive toa positive polarity of audio output signal V_(OUT), the at least oneswitching device for providing the negative polarity voltage operates ata second current less than the first current. Accordingly, audio IC 9may utilize output signal polarity information to provide reduction inpower consumption of a charge pump power supply, as compared withtraditional approaches.

Referring now to FIG. 3 and additionally with reference to FIGS. 4A-4D,details of an example charge pump power supply 10 are depicted, inaccordance with embodiments of the present disclosure. When a firstoperating mode (Mode 1) of charge pump power supply 10 is selected, asmay be indicated by the MODE SELECT signal set in the logical high (“1”)state, switch S8 may close, and the voltage VBATT+ may be applieddirectly to the positive polarity terminal (OUT+) of charge pump powersupply 10. FIGS. 4A and 4B show an equivalent circuit arrangement forMode 1 in first and second clock phases, respectively, omitting openswitches and inactive circuit components. Switches S1, S2 and S4 areopen and not activated in the first operating mode, as logical AND gatesAND10 and AND11 disable the control signals to switches S1, S2 and S4,and the inverted Mode Select signal provided by inverter I10 is in alogical low (“0”) state. For a single-ended (unipolar) power supply,capacitors C12-C13, switches S3, S6, and S7 may be omitted. Asillustrated in FIGS. 4A and 4B, in Mode 1, the positive power supplyvoltage at the positive polarity terminal is supplied directly from thepositive input terminal VBATT+.

To produce the negative output supply voltage in mode 1, the inputvoltage provided between input terminals VBATT+ and VBATT− is invertedby a voltage inverter. In phase one (φ₁) of Mode 1, switches S3 and S6may be closed, which may charge capacitor C12 by connection across inputterminals VBATT+ and VBATT−, as illustrated in FIG. 4A. In phase two(φ₂) of mode 1, switch S3 and switch S6 may open and switch S5 andswitch S7 may close, which may reverse the terminal of capacitor C12applied to the VBATT− input terminal. Switch S7 may apply the terminalof capacitor C12 that was applied to the VBATT− input terminal in phaseone, to the negative polarity terminal (OUT−), as further illustrated byFIG. 4B. The switching action described above provides a negativevoltage at the negative polarity terminal with respect to the VBATT−terminal that is substantially equal to the magnitude of the voltagebetween the positive polarity terminal and the VBATT− terminal, whichacts as the reference midpoint voltage (ground) at the junction betweenoutput capacitors C11 and C13.

In a second operating mode (Mode 2), which may be active when the MODESELECT signal is in the logical low (“0”) state, switch S8 may beopened. In phase one (φ₁) of Mode 2, switches S1 and S4 may be closed,which may apply capacitor C10 in series with output capacitor C11 acrossthe VBATT+ and VBATT− terminals, as further illustrated in FIG. 4C. Inphase two (φ₂) of Mode 2, switches S1 and S4 may be opened and switchesS2 and S5 may be closed, which may couple capacitor C10 in parallel withcapacitor C11 as further illustrated in FIG. 4D. Because the secondphase of mode 2 equalizes the voltage on capacitors C10 and C11, thestable operating point of the circuit may be such that the input voltagebetween the VBATT+ and VBATT− terminals will be split equally during thecharging phase, irrespective of the relative capacitance of C10 and C11.Thus the voltage at the positive polarity output terminal in Mode 2 willbe half of the voltage across the VBATT+ and VBATT− terminals. Otherratios can be constructed by switching more capacitors in series withcapacitors C10 and C11 during phase one, and connecting them all inparallel during phase two. For example, a voltage of one third of theinput battery voltage may be produced by using three capacitorsconnected alternatively in series across the battery terminals andparallel between the positive polarity terminal and the VBATT− terminal.

The negative supply in the second operating mode (Mode 2) may beprovided in a manner similar to that of the first operating mode and theconnections of capacitor C12 are shown in FIG. 4B and FIG. 4D, as beingthe same. However, as illustrated in FIG. 4C, because switch S8 is openin the second operating mode, during phase one of Mode 2, capacitor C12is charged from the positive polarity terminal rather than the VBATT+terminal as was shown in FIG. 4A for Mode 1. Switch S4 may perform theoperation of connecting capacitor C12 to the positive polarity terminal,as illustrated in FIG. 4C, along with the above-described operation ofapplying capacitor C10 in series with capacitor C11 in phase one for thepositive power supply and therefore the relative phases between thevoltage inverter supplying the negative polarity terminal voltage andthe circuit supplying the positive polarity terminal voltage must bemaintained in the depicted configuration. Otherwise, eight switches maybe utilized and the common connection between capacitor C10 and C12broken. The additional switch may be provided between capacitor C12 andthe positive polarity terminal, and would be active in Mode 2, phase 1.It is also possible to further reduce the number of switches from sevento six, by removing switch S3 and controlling switch S4 with theunqualified (φ₁) signal. However, the inclusion of switch S3 may reducethe impedance of the power supply path in the first operating mode,which may be the highest voltage/current operating mode. Therefore, itmay generally be advantageous to include switch S3 in the circuit.

In some embodiments, switches of the switching circuit integral tocharge pump power supply 10 may be operated at a particular frequencybased on a magnitude of audio output signal V_(OUT). Turning again toFIG. 2, audio IC 9 may include an envelope detector 20 and a clockgenerator 22. Envelope detector 20 may comprise any system, device, orapparatus configured to detect when digital audio input signal DIG_IN(or another signal indicative of audio output signal V_(OUT)) is withina predetermined threshold of its maximum or minimum full-rangemagnitude, and generate a signal PEAK_DETECT when such signal indicativeof audio output signal V_(OUT) is within such threshold. Clock generator22 may be any system, device, or apparatus (e.g., phase-locked loop,delay-locked loop, etc.) configured to generate one or more periodicclock signals (e.g., signals CLK and CLK2). In some embodiments, theclock signal CLK generated by clock generator 22 may be of a firstfrequency when signal PEAK_DETECT is asserted and a second frequencylesser than the first frequency when signal PEAK_DETECT is not asserted.Thus, where magnitude of audio output signal V_(OUT) approaches eitherof the positive polarity voltage or negative polarity voltage ofV_(SUPPLY) (as indicated by the signal PEAK_DETECT which is generatedfrom digital audio input signal DIG_IN or another signal indicative ofaudio output signal V_(OUT)), switches for switching one or morecapacitors providing the particular polarity of supply voltageV_(SUPPLY) may switch at a greater frequency relative to that in whichthe magnitude of audio output signal V_(OUT) is not near either of thepositive polarity voltage or negative polarity voltage of supply voltageV_(SUPPLY). Thus, responsive to a magnitude of a difference betweenaudio output signal V_(OUT) and the positive polarity voltage of supplyvoltage V_(SUPPLY) being less than a predetermined threshold, chargepump power supply 10 may operate the switches for switching one or morecapacitors providing the positive polarity voltage of supply voltageV_(SUPPLY) at a first frequency, and responsive to the magnitude ofdifference between audio output signal V_(OUT) and the positive polarityvoltage of supply voltage V_(SUPPLY) being greater than thepredetermined threshold, charge pump power supply 10 may operate theswitches for switching one or more capacitors providing the positivepolarity voltage of supply voltage V_(SUPPLY) at a second frequency lessthan the first frequency. Similarly, responsive to a magnitude of adifference between audio output signal V_(OUT) and the negative polarityvoltage of supply voltage V_(SUPPLY) being less than a predeterminedthreshold, charge pump power supply 10 may operate switches forswitching one or more capacitors providing the negative polarity voltageof supply voltage V_(SUPPLY) at a first frequency, and responsive to themagnitude of the difference between audio output signal V_(OUT) and thenegative polarity voltage of supply voltage V_(SUPPLY) being greaterthan the predetermined threshold, charge pump power supply 10 mayoperate the switches for switching one or more capacitors providing thenegative polarity voltage of supply voltage V_(SUPPLY) at a secondfrequency less than a first frequency. Accordingly, audio IC 9 mayutilize output signal magnitude information to provide reduction inpower consumption of a charge pump power supply, as compared withtraditional approaches.

As described in greater detail elsewhere in this disclosure, charge pumppower supply 10 may include a plurality of capacitors and a switchingcircuit for switching the capacitors to provide supply voltageV_(SUPPLY) in accordance with the select input. In addition, switches ofthe switching circuit may be operated based on the polarity of audiooutput signal V_(OUT). For example, responsive to the signal polaritysignal indicating a positive polarity of the output signal, switches forswitching one or more capacitors providing a positive polarity of supplyvoltage V_(SUPPLY) in a particular operating mode of charge pump powersupply 10 may be configured to switch at a greater frequency thanswitches for switching one or more capacitors providing a negativepolarity of supply voltage V_(SUPPLY) in the particular operating mode.Conversely, responsive to the signal polarity signal indicating anegative polarity of the output signal, switches for switching one ormore capacitors providing the negative polarity of supply voltageV_(SUPPLY) in the particular operating mode of charge pump power supply10 may be configured to switch at a greater frequency than switches forswitching one or more capacitors providing the positive polarity ofsupply voltage V_(SUPPLY) in the particular operating mode. To furtherillustrate, as shown in FIG. 3, two or more clock signals comprisingsignals CLK and CLK2, may be provided to charge pump power supply 10,wherein the frequency of CLK may be greater than that of CLK2. Thus, inMode 1 described above, when audio output signal V_(OUT) has a positivepolarity, switch S8 may be clocked by signal CLK and switches S3, S6,S5, and S7 may be clocked by signal CLK2, and when audio output signalV_(OUT) has a negative polarity, switch S8 may be clocked by signal CLK2and switches S3, S6, S5, and S7 may be clocked by signal CLK. Similarly,in Mode 2 described above, when audio output signal V_(OUT) has apositive polarity, switches S1, S2, and S4 may be clocked by signal CLKand switches S6, S5, and S7 may be clocked by signal CLK2, and whenaudio output signal V_(OUT) has a negative polarity, switches S2 and S4may be clocked by signal CLK2 and switches S1, S6, S5, and S7 may beclocked by signal CLK. In Mode 2, switch S1 may be clocked by thehigher-frequency clock CLK for either polarity of audio output signalV_(OUT), as switch S1 is used to provide both the positive polarity andnegative polarity of power supply voltage V_(SUPPLY) in Mode 2.Accordingly, audio IC 9 may utilize output signal polarity informationto provide reduction in power consumption of a charge pump power supply,as compared with traditional approaches.

Also as described elsewhere in this disclosure, based on the polarity ofaudio output signal V_(OUT), charge pump power supply 10 may generate apositive polarity voltage of supply voltage V_(SUPPLY) of a particularmagnitude relative to the common-mode voltage of charge pump powersupply 10 and a negative polarity voltage of supply voltage V_(SUPPLY)of a different magnitude relative to the common-mode voltage. Toillustrate, in particular embodiments charge pump power supply 10 mayoperate in a first mode (“Mode A”) in which it generates a maximumpositive polarity voltage of V_(MAX) and a minimum negative polarityvoltage of −V_(MAX), and may operate in a second mode (“Mode B”) inwhich it generates a maximum positive polarity voltage of V_(MAX)/2 anda minimum negative polarity voltage of −V_(MAX)/2. When charge pumppower supply 10 is operating in Mode A (in accordance with the modeselect signal), charge pump power supply 10 may generate a negativepolarity voltage of −V_(MAX) and a positive polarity voltage ofV_(MAX)/2 when the audio output signal V_(OUT) has a negative polarity,and thus have an equivalent circuit arrangement similar or identical tothat shown in FIG. 5A for phase one (φ₁) of Mode A and an equivalentcircuit arrangement similar or identical to that shown in FIG. 5B forphase two (φ₂) of Mode A. When charge pump power supply 10 is operatingin Mode A (in accordance with the mode select signal), charge pump powersupply 10 may generate a positive polarity voltage of V_(MAX) and anegative polarity voltage of −V_(MAX)/2 when the audio output signalV_(OUT) has a positive polarity, and thus may have an equivalent circuitarrangement similar or identical to that shown in FIG. 5C for phase one(φ₁) of Mode A and an equivalent circuit arrangement similar oridentical to that shown in FIG. 5D for phase two (φ₂) of Mode A. Withrespect to FIGS. 5C and 5D, switches S9 and S10 and capacitor C14 arepresent which are not depicted in FIG. 3. Thus, in embodiments wherecharge pump power supply 10 operates in response to a polarity of audiooutput signal V_(OUT), charge pump power supply depicted in FIG. 3 maybe modified to include switches S9 and S10 and capacitor C14.

When charge pump power supply 10 is operating in Mode B (in accordancewith the mode select signal), charge pump power supply 10 may generate apositive polarity voltage of V_(MAX)/2 and a negative polarity voltageof −V_(MAX)/2 regardless of the polarity of audio output signal V_(OUT),and thus may have an equivalent circuit arrangement similar or identicalto that shown in FIG. 4C for phase one (φ₁) of Mode B and an equivalentcircuit arrangement similar or identical to that shown in FIG. 4D forphase two (φ₂) of Mode B.

Accordingly, in the embodiments where charge pump power supply 10operates in response to a polarity of audio output signal V_(OUT), whenthe polarity of audio output signal V_(OUT) is positive, a magnitude ofa difference between the positive polarity voltage and the common-modevoltage may be equal to a particular mode-dependent voltage and amagnitude of a difference between the negative polarity voltage and thecommon-mode voltage may be substantially equal to a rational fraction ofthe particular mode-dependent voltage, while when the polarity of audiooutput signal V_(OUT) is negative, a magnitude of a difference betweenthe negative polarity voltage and the common-mode voltage may be equalto a particular mode-dependent voltage and a magnitude of a differencebetween the positive polarity voltage and the common-mode voltage may besubstantially equal to a rational fraction of the particularmode-dependent voltage. In such embodiments, the various logic gates(e.g., AND gates) of charge pump power supply 10 may be configured toprovide for different magnitude of voltages being supplied to theoutputs of charge pump power supply 10. Accordingly, audio IC 9 mayutilize output signal polarity information to provide reduction in powerconsumption of a charge pump power supply, as compared with traditionalapproaches.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the exemplary embodiments herein thata person having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to theexemplary embodiments herein that a person having ordinary skill in theart would comprehend. Moreover, reference in the appended claims to anapparatus or system or a component of an apparatus or system beingadapted to, arranged to, capable of, configured to, enabled to, operableto, or operative to perform a particular function encompasses thatapparatus, system, or component, whether or not it or that particularfunction is activated, turned on, or unlocked, as long as thatapparatus, system, or component is so adapted, arranged, capable,configured, enabled, operable, or operative.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the invention andthe concepts contributed by the inventor to furthering the art, and areconstrued as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present inventionshave been described in detail, it should be understood that variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the disclosure.

1. An audio amplifier circuit for providing an output signal to an audiotransducer, the audio amplifier circuit comprising: a power amplifierhaving an audio input for receiving an audio input signal, an audiooutput for providing the output signal, and a power supply input; and acharge pump power supply for providing a power supply voltage to thepower supply input, wherein the power supply voltage has a firstpolarity voltage relative to a common-mode voltage and a second polarityvoltage relative to the common-mode voltage such that the power supplyvoltage equals a difference between the first polarity voltage and thesecond polarity voltage, wherein: the charge pump power supply has asignal polarity input for indicating a polarity of the output signal;and switches for switching one or more capacitors providing the firstpolarity voltage are configured to switch in a first sequence such thatelectrical charge is transferred from the one or more capacitorsproviding the first polarity voltage at a greater rate than a rate oftransfer of electrical charge from the one or more capacitors providingthe second polarity voltage.
 2. The audio amplifier circuit of claim 1,further comprising a control circuit for generating the signal polarityinput based on the polarity of the output signal.
 3. The audio amplifiercircuit of claim 2, wherein the control circuit determines the polarityof the output signal based on a sign bit of a digital audio inputsignal.
 4. The audio amplifier circuit of claim 2, wherein: the poweramplifier further comprises at least one driving device for generatingthe output signal based on the audio input signal; and the controlcircuit determines the polarity of the output signal based on a ratio ofload current to quiescent current in the at least one driving device. 5.The audio amplifier circuit of claim 2, wherein: the charge pump powersupply further comprises an input for receiving a source voltage; andthe control circuit determines the polarity of the output signal basedon a voltage difference between the power supply voltage and the sourcevoltage.
 6. (canceled)
 7. The audio amplifier circuit of claim 1,wherein: responsive to a magnitude of a difference between the outputsignal and the first polarity voltage being less than a predeterminedthreshold, the charge pump power supply operates the switches forswitching one or more capacitors providing the first polarity voltage ata first frequency; and responsive to the magnitude of the differencebetween the output signal and the first polarity voltage being greaterthan the predetermined threshold, the charge pump power supply operatesthe switches for switching one or more capacitors providing the firstpolarity voltage at a second frequency less than the first frequency. 8.The audio amplifier circuit of claim 1, wherein: responsive to amagnitude of a difference between the output signal and the secondpolarity voltage being less than a predetermined threshold, the chargepump power supply operates the switches for switching one or morecapacitors providing the second polarity voltage at a first frequency;and responsive to the magnitude of the difference between the outputsignal and the second polarity voltage being greater than thepredetermined threshold, the charge pump power supply operates theswitches for switching one or more capacitors providing the secondpolarity voltage at a second frequency less than the first frequency. 9.The audio amplifier circuit of claim 1, wherein: the power amplifierincludes at least one switching device for generating a first polarityof the output signal and at least one switching device for generating asecond polarity of the output signal based on the audio input signal;responsive to the signal polarity input indicating a positive polarityof the output signal, the at least one switching device for providingthe first polarity voltage operates at a first current; and responsiveto the signal polarity input indicating a negative polarity of theoutput signal, the at least one switching device for providing the firstpolarity voltage operates at a second current less than the firstcurrent.
 10. The audio amplifier circuit of claim 1, wherein: the poweramplifier includes at least one switching device for generating a firstpolarity of the output signal and at least one switching device forgenerating a second polarity of the output signal based on the audioinput signal; responsive to the signal polarity input indicating anegative polarity of the output signal, the at least one switchingdevice for providing the second polarity voltage operates at a firstcurrent; and responsive to the signal polarity input indicating apositive polarity of the output signal, the at least one switchingdevice for providing the second polarity voltage operates at a secondcurrent less than the first current.
 11. The audio circuit of claim 1,wherein the power supply voltage is a single-ended voltage referenced toa ground voltage in which the common-mode voltage is equal to one-halfof a maximum power supply voltage and the second polarity voltage has aminimum equal to the ground voltage.
 12. The audio circuit of claim 1,wherein the power supply voltage is a differential voltage in which thecommon-mode voltage is equal to a mean of a maximum first polarityvoltage and a minimum second polarity voltage.
 13. A method forproviding an output signal to an audio transducer, comprising: providingby a charge pump power supply a power supply voltage to a power supplyinput of a power amplifier having an audio input for receiving an audioinput signal and an audio output for providing the output signal,wherein: the power supply voltage has a first polarity voltage relativeto a common-mode voltage and a second polarity voltage relative to thecommon-mode voltage such that the power supply voltage equals adifference between the first polarity voltage and the second polarityvoltage, wherein: the charge pump comprises a plurality of capacitorsand a switching circuit for switching the capacitors to provide thefirst voltage or the second voltage in accordance with the select input;and the charge pump power supply has a signal polarity input forindicating a polarity of the output signal; and switching switches forswitching one or more capacitors providing the first polarity voltage ina first sequence such that electrical charge is transferred from the oneor more capacitors providing the first polarity voltage at a greaterrate than a rate of transfer of electrical charge from the one or morecapacitors providing the second polarity voltage.
 14. The method ofclaim 13, further comprising generating the signal polarity input basedon the polarity of the output signal.
 15. The method of claim 14,further comprising determining the polarity of the output signal basedon a sign bit of a digital audio input signal.
 16. The method of claim14, wherein: the power amplifier further comprises at least one drivingdevice for generating the output signal based on the audio input signal;and determining the polarity of the output signal further comprisesdetermining the polarity based on a ratio of load current to quiescentcurrent in the at least one driving device.
 17. The method of claim 14,wherein: the charge pump power supply further comprises an input forreceiving a source voltage; and determining the polarity of the outputsignal further comprises determining the polarity based on a voltagedifference between the power supply voltage and the source voltage. 18.(canceled)
 19. The method of claim 13, further comprising: responsive toa magnitude of a difference between the output signal and the firstpolarity voltage being less than a predetermined threshold, operatingthe switches for switching one or more capacitors providing the firstpolarity voltage at a first frequency; and responsive to the magnitudeof the difference between the output signal and the first polarityvoltage being greater than the predetermined threshold, operating theswitches for switching one or more capacitors providing the firstpolarity voltage at the second frequency less than a first frequency.20. The method of claim 13, further comprising: responsive to amagnitude of a difference between the output signal and the secondpolarity voltage being less than a predetermined threshold, operatingthe switches for switching one or more capacitors providing the secondpolarity voltage at a first frequency; and responsive to the magnitudeof the difference between the output signal and the second polarityvoltage being greater than the predetermined threshold, operating theswitches for switching one or more capacitors providing the secondpolarity voltage at the second frequency less than a first frequency.21. The method of claim 13, further comprising: responsive to the signalpolarity input indicating a positive polarity of the output signal,operating the at least one switching device for providing the firstpolarity voltage at a first current; and responsive to the signalpolarity input indicating a negative polarity of the output signal,operating the at least one switching device for providing the firstpolarity voltage at a second current less than the first current. 22.The method of claim 13, further comprising: responsive to the signalpolarity input indicating a negative polarity of the output signal,operating the at least one switching device for providing the secondpolarity voltage at a first current; and responsive to the signalpolarity input indicating a positive polarity of the output signal,operating the at least one switching device for providing the secondpolarity voltage at a second current less than the first current. 23.The method of claim 13, wherein the power supply voltage is asingle-ended voltage referenced to a ground voltage in which thecommon-mode voltage is equal to one-half of a maximum power supplyvoltage and the second polarity voltage has a minimum equal to theground voltage.
 24. The method of claim 13, wherein the power supplyvoltage is a differential voltage in which the common-mode voltage isequal to a mean of a maximum first polarity voltage and a minimum secondpolarity voltage.
 25. The method of claim 13, further comprisingswitching switches for switching one or more capacitors providing thefirst polarity voltage in the first sequence responsive to the signalpolarity input indicating a positive polarity of the output signal. 26.The method of claim 13, further comprising switching the switches forswitching the one or more capacitors providing the first polarityvoltage in a second sequence such that electrical charge is transferredfrom the one or more capacitors providing the first polarity voltage ata lesser rate than the rate of transfer of electrical charge from theone or more capacitors providing the second polarity voltage.
 27. Themethod of claim 16, further comprising: switching the switches forswitching the one or more capacitors providing the first polarityvoltage in the first sequence responsive to the signal polarity inputindicating a positive polarity of the output signal; and switching theswitches for switching the one or more capacitors providing the firstpolarity voltage in the second sequence responsive to the signalpolarity input indicating a negative polarity of the output signal. 28.The audio amplifier circuit of claim 1, wherein the switches forswitching one or more capacitors providing the first polarity voltageare configured to switch in the first sequence responsive to the signalpolarity input indicating a positive polarity of the output signal. 29.The audio amplifier circuit of claim 1, wherein the switches forswitching the one or more capacitors providing the first polarityvoltage are configured to switch in a second sequence such thatelectrical charge is transferred from the one or more capacitorsproviding the first polarity voltage at a lesser rate than the rate oftransfer of electrical charge from the one or more capacitors providingthe second polarity voltage.
 30. The audio amplifier circuit of claim29, wherein: the switches for switching the one or more capacitorsproviding the first polarity voltage are configured to switch in thefirst sequence responsive to the signal polarity input indicating apositive polarity of the output signal; and the switches for switchingthe one or more capacitors providing the first polarity voltage areconfigured to switch in the second sequence responsive to the signalpolarity input indicating a negative polarity of the output signal. 31.An audio amplifier circuit for providing an output signal to an audiotransducer, the audio amplifier circuit comprising: a power amplifierhaving an audio input for receiving an audio input signal, an audiooutput for providing the output signal, and a power supply input; and acharge pump power supply for providing a power supply voltage to thepower supply input, wherein the power supply voltage has a firstterminal with a first polarity voltage relative to a common-mode voltageand a second terminal with a second polarity voltage relative to thecommon-mode voltage such that the power supply voltage equals adifference between the first polarity voltage and the second polarityvoltage, wherein: the charge pump comprises a plurality of capacitorsand a switching circuit comprising a plurality of switches for switchingthe capacitors to provide the power supply voltage; switches forswitching one or more capacitors providing the first polarity voltage tothe first terminal are configured to switch with a first switchingsequence and at a first frequency based on a first current drawn by thepower amplifier from the first terminal; and switches for switching oneor more capacitors providing the second polarity voltage to the secondterminal are configured to switch with a second switching sequence andat a second frequency based on a second current drawn by the poweramplifier from the second terminal.
 32. The audio amplifier circuit ofclaim 31, wherein: the charge pump power supply has a signal polarityinput for indicating a polarity of the output signal; and the chargepump power supply is configured to output a first polarity voltage and asecond polarity voltage such that: when the polarity of the outputsignal is of a first polarity, a magnitude of difference between thefirst polarity voltage and the common-mode voltage is greater than amagnitude of difference between the second polarity voltage and thecommon-mode voltage; and when the polarity of the output signal is of asecond polarity, a magnitude of difference between the first polarityvoltage and the common-mode voltage is lesser than a magnitude ofdifference between the second polarity voltage and the common-modevoltage.
 33. A method for providing an output signal to an audiotransducer, comprising: providing by a charge pump power supply a powersupply voltage to a power supply input of a power amplifier having anaudio input for receiving an audio input signal and an audio output forproviding the output signal, wherein the power supply voltage has afirst polarity voltage relative to a common-mode voltage and a secondpolarity voltage relative to the common-mode voltage such that the powersupply voltage equals a difference between the first polarity voltageand the second polarity voltage, and wherein the charge pump comprises aplurality of capacitors and a switching circuit comprising a pluralityof switches for switching the capacitors to provide the power supplyvoltage; switching switches for switching one or more capacitorsproviding the first polarity voltage with a first switching sequence andat a first frequency based on a first current drawn by the poweramplifier from the first terminal; and switching switches for switchingone or more capacitors providing the first polarity voltage with asecond switching sequence and at a second frequency based on a secondcurrent drawn by the power amplifier from the second terminal.
 34. Themethod of claim 33, wherein the charge pump power supply has a signalpolarity input for indicating a polarity of the output signal andfurther comprising outputting the first polarity voltage and the secondpolarity voltage by the charge pump power supply such that: when thepolarity of the output signal is of a first polarity, a magnitude ofdifference between the first polarity voltage and the common-modevoltage is greater than a magnitude of difference between the secondpolarity voltage and the common-mode voltage; and when the polarity ofthe output signal is of a second polarity, a magnitude of differencebetween the first polarity voltage and the common-mode voltage is lesserthan a magnitude of difference between the second polarity voltage andthe common-mode voltage.